They're actually skipping it, not just "not doing a live dog and pony show" like a decade ago.
Nintendo has officially confirmed news rumored at the end of January: it will not have a presence at the revived E3 expo.
In a statement to VentureBeat, Nintendo said "We approach our involvement in any event on a case-by-case basis and are always considering various ways to engage with our fans. Since this year’s E3 show didn’t fit into our plans, we have made the decision to not participate" before reiterating their support for the show and its original organizer, the Electronic Software Association (ESA).
E3 2023 was to be the first event organized by ReedPop (who run the PAX expos) following three years of no in-person events due to various permutations of the ongoing COVID-19 pandemic. Nintendo was the only console manufacturer to be on the show floor proper at the last in-person, ESA-organized event in 2019, with Microsoft holding their booth at the Microsoft Theater near the Los Angeles Convention Center and Sony skipping the show entirely.
The lack of an E3 does not preclude Nintendo having a Nintendo Direct presentation in June to set up the second half of 2023, as there are no confirmed launch dates for first party Switch software following the launch of Pikmin 4 on July 21.